of s now, below the fros tha rdene d soil, in crevices in the bark of trees, and in sheltered caves,
the paras ites and the predators have found ways to tide themselves over the seas on of cold.
The eggs of the mantis are s ecure in little cas es of thin parchme nt attached to the branch of a
s hrub by the mothe r who lived her life s pan with the s ummer that is gone.
The female Polistes was p, taking s helter in a forgotten corner of s ome attic, carries in her body
the fertilized eggs, the heritage on which the whole future of her colony de pends. She, the lone
survivor, will start a small paper nest in the spring, lay a few eggs in its cells, and carefully rear a
s mall force of worke rs. With their help s he will then enlarge the nes t and de velop the colony.
Then the worke rs , foraging ceas eless ly through the hot days of s umme r, will des troy countles s
caterpillars. Thus , through the circums tances of their lives , and the nature of our own wants , all
these have been our allies in keeping the balance of nature tilted in our favor. Yet we have
turned our artillery agains t our friends. The terrible danger is that we have grossly
unde res timated their value in keeping at bay a dark tide of enemies that, without thei r help,
can overrun us.
The pros pect of a general and permane nt lowe ring of environmental res is tance becomes grimly
and increasingly real with each pass ing year as the numbe r, variety, and des tructivenes s of
insecticides grows. With the passage of time we may expect progressively more serious
outbreaks of insects , both dis eas e-carrying and crop-des troying s pecies , in excess of anything
we have ever known. ‘Yes, but isn’t this all theoretical?’ you may ask. ‘Surely it won’t really
happen—not in my lifetime, anyway.’ But it is happening, here and now. Scientific journals had
already recorded some 50 species involved in violent dislocations of nature’s balance by 1958.
More examples are being found every year. A recent review of the subject contained references
to 215 papers reporting or dis cuss ing unfavorable ups ets in the balance of ins ect populations
caus ed by pes ticides.
Sometimes the res ult of che mical s praying has been a treme ndous ups urge of the ve ry ins ect
the s praying was intended to control, as when blackflies in Ontario became 17 times more
abundant after s praying than they had been bef ore. Or whe n in England an enormous outbreak
of the cabbage aphid—an outbreak that had no parallel on record—followe d s praying with one
of the organic phos phorus chemicals. At other times spraying, while reasonably effective
against the target insect, has let loose a whole Pandora’s box of des tructive pes ts that had
never previous ly been abundant enough to caus e trouble. The s pider mite, for example, has
become practically a worldwide pest as DDT and other insecticides have killed off its enemies.
The s pider mite is not an insect. It is a barely visible eight-legged creature belonging to the
group that includes s piders , s corpions , and ticks. It has mouth parts adapted for piercing and
s ucking, and a prodigious appetite for the chlorophyll that makes the world green. It ins erts
thes e minute and s tiletto-s harp mouth parts into the oute r cells of leaves and evergreen
needles and extracts the chlorophyll. A mild infes tation gives trees and s hrubbery a mottled or
salt-and-pepper appearance; wi th a heavy mite population, foliage turns yellow and falls.
This is what happened in s ome of the wes tern nati onal fores ts a few years ago, when in 1956
the Unite d States Fores t Se rvice s prayed s ome 88 5,000 acres of fores ted lands with DDT. The
intention was to control the s pruce budworm, but the following summer it was discovered that
a problem wors e than the budworm da mage had been c reated. I n s urveying t he fo res ts from
the air, vas t blighted areas could be s een where the magnificent Douglas firs were turning
brown and dropping their needles. In the Helena National Fores t and on the wes tern s lopes of
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